A. Field of the Invention
The present invention relates, in general, to an improvement of the Asymmetric Incremental Sheet Forming (AISF) technology, and more particularly to an improved Asymmetric Incremental Sheet Forming (AISF) apparatus or method for easier and more accurately forming of sheet material of various composition. More particularly the invention is related to a system and method for asymmetric incrementally forming a sheet material blank by means of a locoregional heat/cooling system that is synchronised with the movement of the forming tool. The sheet material is at the same time locally heated at the contact zone of the forming means by a dynamically moving heating source that moves synchronically with the movement of the forming means over the surface of the sheet material to locally increase plasticity of the sheet material only at the contact zone of the forming tool or just in front or next to the contact zone of the forming tool on its movement toolpath.
B. Description of the Related Art
Incremental forming is the process of forming sheet material into complicated shapes without the use of either male or female dies. The method uses a single point means which plastically deforms sheet material, which is clamped in a blank holder to provide a localised deformation. The final shape of the part can for instance be obtained by the relative movement of a simple and small forming tool with respect to the blank. By incrementally moving the forming tool over the sheet using a controllable positioning system, for instance a computer numerically controlled tool, the plastically deformed points are, in effect, added as a means moves to provide a final shape.
Many different implementations of the incremental forming method exist. Single Point Incremental Forming uses a simple forming tool, preferably a hemispherical tool, to deform a sheet material clamped within a forming rig, and most preferably a metal rod with a smooth hemispherical tip, for instance within the range of 9-30 mm (FIG. 2). Two Point Incremental Forming also uses as forming tool a simple hemispherical tool to deform a sheet material clamped into a forming rig. The difference lies in the fact that under the sheet material a partial die is located and that the rig is allowed to translate along the bushings in the direction of the forming tool (FIG. 3). Other implementations exist as well where a hammering device or shot peening device replaces the forming tool. The forming tool can be controlled using a CNC milling machine, a robot or any other device that allows for the exact positioning of the forming tool.
The forming tool used is in many cases a simple hemispherical tool. There is no need for the forming tools to be adapted to the part to be formed. With a basic set of tools one is capable of forming a wide variety of desired part geometries.
This method of incremental forming, in the present state of the art, is suitable for incremental forming of soft materials such as aluminium and steels with a low carbon content 0.05% to 0.26% (e.g. AISI 1018 steel). The method, however, has the drawback that the forces on the forming means become high when forming thicker material or material with high yield strength and low ductility. For instance if the content of carbon rises in alloys of iron and carbon, the metal becomes harder and stronger but less ductile and it is more difficult to shape the alloy sheet with an asymmetric incremental sheet forming (AISF) apparatus.
Furthermore, it is generally not possible to substantially form harder and stronger but less ductile materials such as the alloys of iron and carbon for instance medium carbon steel: 0.29% to 0.54% (e.g. AISI 1040 steel), high carbon steel: 0.55% to 0.95%, very high carbon steel: 0.96% to 2.1% or the Titanium Grade 5 or Magnesium sheet materials. Yet another drawback is the difficulty to create clearly localised slope changes within parts. Should this slope change be located near the edge of the part this problem could be solved by using backing plates. This backing plate supports the region of the sheet material blank that should not be plastically deformed (see FIG. 2). These backing plates are cumbersome to work with and very difficult to use when the sudden slope change is not located near the edge of the plate.
Thus, there is a need in the art for improving the methods of incremental forming. The present invention provides an improvement to these drawbacks by using a method to incrementally form a sheet material blank that is at the same time locally heated by a dynamically moving heat source.